Goodwin/Moroso NC Coolant Expansion Tank

This post could also be titled – Keeping the NC Engine From Exploding.

Shiny metal goodness.

In the past couple weeks, I’ve learned a lot of trivia about NC Miatas. Facts such as – the coolant bottle in the NC is pressurized. And also – said pressurized coolant expansion tank is prone to cracking and failing after a random number of miles. Sometimes it’s a high mileage like 140k. Sometimes it’s quite low like 14k.

I learned this after driving an unknown NC with 155k on the clock across the desert for 300 miles.

Even better! If and when the bottle explodes, you basically lose the NC’s engine. It apparently cannot take a single overheat.

WTF?

Sight glass.

Even more interesting is the fact that a solution for the problem did not exist until around December of 2016. That’s a full decade after the NC started production.

Insane.

The past solution to the exploding overflow bottle was to kinda “watch it” and replace it with a new one when it starts to turn from white to yellow. If they get orange or brown, you’re living on borrowed time. And NC owners lived like this throughout the time while the car was being made.

Enter the metal bottle done by Moroso and Goodwin Racing. No more expansion tank explosions.

Stock NB pressure cap fits right on top.

This is a very nicely welded piece. It’s got internal baffles just like the stock bottle. It bolts on just like stock and has all of the correct hose outlets. It’s also got a nice sight glass so that you can see if there’s anything inside the little metal bottle.

It costs about 4x the price of a new plastic bottle from Mazda. But it should be a lifetime part without any failure points.

Worth it!

Ready to get fixed.

Since I’ve owned it (almost 2 weeks now), the Stormtrooper has been having some heat problems. As in cabin heat. Randomly, no heat comes out of the fan. That means there’s a bubble somewhere in the heater that needs to be purged. That means jacking the car up.

Always be safe. Use as high quality a jack stand as you can find and afford.

Old bottle screw points.

The bottle is held in by 3 nuts. It’s actually more work to blog about this than to swap out the bottle.

3 bolts with 10mm heads. All on top and not hidden. EASY!

Plugged.

No coolant was really in danger of coming out, but I didn’t wanna take any chances. And I’ve got plenty of 3/8″ socket extensions.

I burped the NC radiator just like I would an NA or NB. I filled the bottle ALL the way up with the car jacked up and added a few inches of distilled water to the funnel. That put the highest water level inside the funnel.

This is not how Miatanet would have you burp an NC radiator. The approved method there is to loosen the big hose and metal tube combo that runs across the back of the engine and try to let some air escape there. This seems insane to me. Making a leak in the cooling system to burp it? It might work very well, but it’s not something I would do with my car.

If anyone reading decides to burp an NC like I did, realize that you’ve gotta siphon some fluid back out of the expansion tank after you’re done. It’s an expansion tank after all and is not meant to be full like a radiator is. Drain it to somewhere on the sight glass or below the “full” mark on the OEM bottle.

Anyways, like I said, I burped the radiator this way. I had no problems. I squeezed the hoses on the back side of the engine and got a lot of big bubbles out. I ran the car for a good 20 minutes and let the thermostat cycle open and closed many times (as seen on my OBDII scanner).

Done!

So much black plastic in that engine bay…

And no exploding coolant bottles to be found anywhere. WOO HOO!!!

After burping, I took a test drive. The engine stayed between 179* and 186*F. (So odd having an ECU that reads in Imperial – Sharka is metric.) No overheating or bad behavior. And the heat blows HOT inside the car!! It’s never been so nice and warm.

It’s become shockingly common lately. But usually they put a screw on plastic cap onto the top of the bottle instead of the flanged metal thing on the NC. The bottle tends to fail right at the cap/bottle interface.

My Mazda3 has a pressurized plastic bottle with a lovely and large screw cap like a coke bottle. No issues.